Electrostatic discharge (ESD) is a common phenomenon that occurs during handling of semiconductor IC (integrated circuit) devices. Electrostatic charges may accumulate for various reasons and cause damage to an IC device. Typically, damage can occur during a testing phase of the IC fabrication, during assembly of the IC to the circuit board, as well as during the use of equipment into which the IC has been installed. The built-up electrostatic charge may be quickly discharged thereby causing significant damage to the IC, e.g. due to dielectric breakdown of oxides and/or due to high levels of conduction through relatively small areas of the circuit arising from reverse breakdown of p-n junctions of the circuit.
To reduce the sensitivity of integrated circuits to electrostatic discharge, integrated circuits with protection devices at their external terminals are designed which provide a “safe” path for the electrostatic charge to follow. Such a safe path is designed in a manner that no damage occurs when electrostatic discharge occurs from a charged body to the integrated circuit. Upon the occurrence of an ESD the built-up electrostatic charge is discharged via the ESD protection device thus preventing damage of the integrated circuit to be protected. For reasons of low cost it is desirable that the fabrication of such a protection device can be integrated into existing process flows. Further, the ESD protection device should reliably avoid damage of the IC device to be protected, at all events and for the whole period of manufacture and use of the integrated circuit.